The present invention relates to a regulating system for a gas turbine plant. Such a gas turbine plant generally comprises a compressed-gas generating unit including a compressor, a combustion chamber and a gas turbine which drives the compressor and constitutes a high pressure turbine stage from which waste gases are conducted to a power turbine. In some instances, the compressed-gas generating unit may comprise simply a combustion chamber fed from an air reservoir. In both instances, however, a regulating valve is provided which is controlled by a control means to control the rate of fuel flow so that, in the event of a loss of load on the power turbine, the fuel flow is decreased, if necessary, to a minimum level which is adequate to keep the unit in idling condition.
If the above-described apparatus for control of the regulating valve should fail for some reason, there is then a real risk that the power turbine would race to high speeds which would be injurious to the equipment, and for this reason a gas turbine plant should be provided with some form of emergency stop means which shuts off the supply of fuel if the speed of the turbine reaches a predetermined level above its normal speed. However, to avoid unnecessary tripping of the emergency stop, the speed level at which tripping occurs should not be chosen at too low an increment above its normal value. On the other hand, this latter requirement means that the speed may reach quite a high value before the tripping actually becomes effective to once again reduce the speed. To avoid this situation, and yet provide security against unnecessary tripping of the emergency stopping apparatus, it is proposed according to the present invention to take into consideration not only the speed of the unit but also its derivative which is of course representative of its angular acceleration, since these two quantities together indicate at a very early stage whether there is a risk of overspeed of the unit.
According to a further embodiment of the invention, the condition of the plant can be monitored in an even safer manner if, in addition to responding to the speed and acceleration of the power turbine, the control apparatus also takes into account a working parameter of the gas unit. In this way, it is possible to ascertain whether the fuel regulating means is operating properly, and it also then becomes able quickly to prevent an overspeed condition. Such apparatus is also then effective in the event that the normal fuel regulating apparatus, although not fully inoperable, is nevertheless not fully effective to prevent an overspeed situation from occurring.